Resin compositions filled with powder reinforcement materials such as inorganic fillers overcome many problems of thermoplastic resins such as rigidity, heat resistance, and dimensional stability with the progress of technical development in recent years, and performance improvement is steadily promoted, and the resin compositions are widely used as industrial members typified by automobile parts. Resins in which the resins after polymerization are powdery and bulky like polyphenylene ether and polyphenylene sulfide are also compounded by kneading machines and utilized in various applications because of their excellent properties.
When a powder thermoplastic resin, or a powder raw material including a large amount of a powder reinforcement material, is melted and kneaded with an extruder, to produce a resin composition, such a powder raw material is poor in biting properties into the extruder because the apparent density is low compared with that of a raw material in a pellet form. Therefore, the output rate achieved is low, and there are many cases where the productivity is low.
For productivity improvement techniques for the method for melting and kneading a powder raw material, those like the following are known.
For example, in Patent Literature 1, a method for producing a resin composition with a twin-screw extruder in which screws having a configuration in which a single-thread screw having wide flight width and kneading disks having a particular twist angle are combined are housed in a barrel, for the purpose of improvement in the productivity of a resin composition containing a filler component at high concentration is described.
In Patent Literature 2, a method fix producing a resin composition with a twin-screw extruder comprising screws having a configuration in which a single-thread screw and particular kneading disks are combined, for the purpose of productivity improvement in the production of a resin composition using a powder raw material is described.
In Patent Literature 3, an extrusion method in which a synthetic resin is melted and kneaded with, for the purpose of an increase in the output rate during the extrusion of a synthetic resin material including a fine powder raw material or a fine powder in a large amount a twin-screw extruder in which an opening that discharges air contained in the above material is provided downstream from the material supply port of a barrel, and without providing such a pressure rise region as to apply strong compression between the material supply port and the opening is described.
In Patent Literature 4, a method for producing a resin composition, in which raw materials are melted and kneaded with a twin-screw kneading extruder under conditions in which the resin pressure in a plasticization region is 1 MPa, or less, for the purpose of improvement in the productivity of a resin composition containing a polypropylene-based resin and an inorganic filler is described.
In Patent Literature 5, a method for producing a resin composition including powdery polyphenylene ether and a thermoplastic resin other than the powdery polyphenylene ether, in which for the purpose of improvement in powdery polyphenylene ether transport capacity, powdery polyphenylene ether is supplied to a molten thermoplastic resin transport region from a side of a twin-screw extruder with a forced side feeder is described. In addition, it is described that in order to prevent a decrease in powdery polyphenylene ether transport capacity, it is preferable to provide an opening hole for gas venting on the upstream side of the upper cover of the extruder barrel at the site where the forced side feeder is connected, and perform gas venting from the opening hole.
However, in all the above production methods, the productivity improvement effect is not sufficient.